Histologic inflammation in the maternal and fetal compartments in a rabbit model of acute intra-amniotic infection

This study was undertaken to determine the course of acute inflammation in the maternal and fetal compartments during experimentally induced ascending intra-amniotic infection.

Forty pregnant rabbits at 70% gestation were inoculated endocervically with 10(5) colony-forming units of Escherichia coli. Does were killed at 0, 4, 8, 16, 24, and 30 hours after inoculation. At necropsy, blood, peritoneal fluid, amniotic fluid, and uterine tissue were cultured. Fetal brain, lung, heart, gut, and kidney were collected for histologic examination. Necrosis, infiltrates, congestion, and edema were each assessed semiquantitatively, and mean composite histologic-inflammation scores were compared with analysis of variance. Inflammation, mitotic activity, and apoptosis were evaluated in the fetal brain, and groups were compared with analysis of variance.

Twenty-six animals were evaluated after 14 were excluded (lack of fever or positive culture results). A significant increase in histologic inflammation score was seen in the uterus (P<.001), placenta(P = .011), and fetal lung (P = .001) but not in other fetal tissues. These changes were seen earlier in the uterus and placenta and later in the fetal lung. Mitotic activity in the fetal brain decreased significantly by 8 hours after cervical inoculation. There was no inflammation in the fetal brain, and apoptosis in the fetal brain did not increase with time.

Histologic inflammation occurs early in both the uterus and the placenta and later in the fetal lung in the rabbit model of acute intra-amniotic infection. This contrasts with the previously reported chronic model of intra-amniotic infection in the rabbit.